When participating in various activities, whether outdoors, on a school campus, in a shopping mall or the like, individuals, particularly children and young adults, would like to know if a friend or companion is nearby. While a large variety of personal locating systems such as a child monitoring system are available, these systems generally do not allow two individuals to monitor the location of each other. Rather, one individual, typically an adult, can monitor the location of a second individual, typically a child, using a low power radio transmitter worn by the child. In relatively simple systems the location of the child is usually monitored so that if the child leaves a predetermined area, the radio transmitter will inform the adult. In other systems the precise location of the child can be determined, but at the expense of a more complex and physically large monitoring unit.
Even in systems in which two or more monitors are employed, each monitor is usually preprogrammed to respond to a companion monitor. That is, the user cannot customize or program one monitor to identify or otherwise respond to other such monitors as the user chooses. For example, U.S. Pat. No. 5,298,883 shows a proximity alert system in which a pair of portable transceiver units transmits a coded signal that is picked up by the other unit. The strength of the received coded signal controls the rate of an audible beeper. The rate of the beeper indicates the approximate distance between companion units.
Accordingly, it would desirable to provide a compact and inexpensive system that is also flexible and programmable, and which alerts individuals equipped with companions units when they come in proximity of one another.